1. Field of the Invention
The present invention relates generally to vehicle integral speedometer and automatic door lock systems and, more specifically, to systems of the type wherein the power door locks automatically lock after the vehicle reaches a predetermined speed.
2. Description of the Prior Art
The prior art teaches using a speed sensor circuit along with a distance sensor transducer coupled to a vehicle drive shaft or to a speed take off of a transmission. The speed sensor circuits generally consist of a digital to analog converting circuit coupled to the distance sensor and activated by a manual door jamb switch. This invention departs from the prior art by utilizing a frequency to voltage converting circuit used for both the speedometer and the automatic door lock system which is less susceptible to a variety of automotive environmental conditions which passive components associated with the digital to analog converting and manual door jamb switches are subjected to. SUMMARY OF THE INVENTION
As a solution to these and other problems, the instant invention comprises an automatic power door lock system which is free from the defects of the prior art. More particularly, the invention comprises an automatic door lock system wherein a relay which powers a door lock automatically energized when a vehicle reaches a predetermined speed. A distance sensor is used to develop a pulse train signal of a pulse-repetition rate proportional to the speed of the vehicle. The distance sensor output signal is coupled to a frequency to voltage circuit which converts the pulse train input signal into complementary sine and cosine waveforms of a varied range of magnitudes and directions. A conventional air-core gauge speedometer employs the sine and cosine waveform signals magnitude and direction information to indicate the speed of the vehicle. A reference point within the range of the complementary waveform is established which, when exceeded in magnitude and direction by the waveforms, a logic signal is developed which activates a relay energizing transistor. The relay is energized only for a chosen duration even though the relay energizing transistor may be turned on.
The invention and its mode of operation will be more fully understood from the following detailed description when taken with the appended drawing figures in which: